Provins is a pretty town in the Ile-de-France, not too far away from Paris and easily reachable in an 80-minute train ride from Paris-Est station. Walking through the narrow streets of the medieval upper town is really a step back in time, and there are many historic buildings, especially churches, all over the town. A visit to Caesar's Tower (actually a medieval building as well) is certainly a highlight and gives you a great impression of an authentic fortification. Its WH designation was controversial and may probably not be entirely justified, but there are certainly worse sites on the list, and a visit to Provins is definitely a nice and memorable experience.